one girl's diary of improvisational engineering

Embedded Bluetooth for $2

This is a continuation of my experiments in bit-banging full-speed USB on the Propeller. I have the basic host controller working reasonably well now, so I started trying to do something a bit more “useful” with it by implementing a simple Bluetooth stack on top of it.

Bluetooth and USB are both quite complicated, and this project is implementing only tiny fractions of each specification. But I think it’s enough to show that the functionality you actually need in a simple embedded application isn’t that complex- and a lot of the cheap consumer electronics you can get nowadays might actually be more hobbyist-accessable than they appear.

Hanno on the forums found some great $2 Bluetooth dongles on DealExtreme. So I just had to order a few of these and try them out with my work-in-progress software stack. The result:

That’s a Propeller demo board, the $2 dongle (stripped down and attached to a 4-pin header, for convenience) and no other components. The demo here is just scanning for nearby devices, but I also have some basic L2CAP support and I’m working on the SDP server. Currently the stack uses 4 cogs (3 for USB, 1 for Bluetooth) and 12 kB of RAM, but I’m hoping to optimize it.

(Of course, this is only possible because the Bluetooth dongle itself has significantly more RAM and ROM than the Propeller has. Oh, the economies of scale!)